G. A. Fett, Dana Corporation Automotive Systems Group, Maumee, OH
In this study six groups of parts were batch carburized, each with a different carbon potential. The parts were hypoid ring and pinion gears made from SAE 8620 steel, net formed differential gears made from SAE 8620R, and U-Notch test bars made from SAE 8620, SAE 4320, and SAE 9310. The carbon potentials used for each batch were 0.2%, 0.4%, 0.6%, 0.8%,1.0%, and 1.2%. The hypoid gears were then fatigue tested, the differential gears were impact and fatigue tested, and the U-Notch bars were tested under slow bend and impact conditions. The results demonstrate that lower carbon potentials are beneficial for fatigue and impact, while higher carbon potentials are beneficial for contact fatigue. However, the fatigue results do vary depending on the grade of steel and whether we are looking at high cycle or low cycle fatigue. This is likely related to the retained austenite content.
Summary: In this study gears and test bars made from various materials were carburized using different carbon potentials. The samples were tested under slow bend, impact, and fatigue. The results demonstrate that in general increasing carbon potential is detrimental to fatigue and impact while it is beneficial to contact fatigue.
